1. Field of the Invention
The present invention relates to a low temperature storage cabinet such as a refrigerator cabinet, a freezer cabinet, a refrigerator/freezer cabinet or the like for storing an article such as foodstuffs, beverages, etc.
2. Description of the Prior Art
There has been proposed a low temperature storage cabinet wherein a heater is embedded in an opening frame structure of the cabinet to prevent the occurrence of dewfall on the surface of the frame structure to be brought into contact with a door hinged to the cabinet body and wherein operation of a compressor is controlled in accordance with an inside temperature of the cabinet to maintain the inside temperature of the cabinet at a predetermined value.
As in the low temperature storage cabinet, the heater for prevention of dewfall in the cabinet is activated during operation of the compressor, the load for cooling the interior of the cabinet is increased due to heat generation of the heater. This causes frequent operation of the compressor, resulting in useless consumption of the electric power.
To solve the problem, proposed in Japanese Patent Laid-open Publications Nos. 6 (1994)-3034, 6 (1994)-3035, 5 (1993)-142845, 5 (1993)-240565 and Japanese Utility Model Laid-open Publications 62 (1987)-16623, 62 (19987)-88277 are various control methods of the heater in relation to operation of the compressor, an outside temperature of the cabinet, a temperature of dewfall or outside humidity of the cabinet. However, in this type of the low temperature storage cabinet, it is required to further decrease the consumption of the electric power caused by activation of the heater for prevention of dewfall in the cabinet.
It is, therefore, a primary object of the present invention to provide a low temperature storage cabinet capable of further decreasing the unnecessary consumption of electric power caused by unneeded activation of the heater.
According to the present invention, the object is accomplished by providing a low temperature storage cabinet which includes a heater embedded in an opening frame structure of the cabinet to prevent the occurrence of dewfall on a surface of the frame structure to be brought into contact with a door hinged to the cabinet body, and a compressor the operation of which is controlled in accordance with an inside temperature of the cabinet to maintain the inside temperature of the cabinet at a predetermined value, wherein the heater is activated synchronously in response to operation of the compressor and is activated in accordance with outside humidity or inside temperature of the cabinet during stopping of the compressor.
In a practical embodiment, the low temperature storage cabinet is provided with an inside temperature sensor for detecting an inside temperature of the cabinet, a humidity sensor for detecting outside humidity of the cabinet, and control means responsive to a detection signal from the inside temperature sensor or humidity sensor for controlling activation of the heater in accordance with the inside temperature or outside humidity of the cabinet.
In another practical embodiment of the present invention, the low temperature storage cabinet is provided with an outside temperature sensor for detecting an outside temperature of the cabinet, a humidity sensor for detecting outside humidity of the cabinet, and control means for calculating a dewfall temperature on the surface of the opening frame structure based on the outside temperature and outside humidity detected by the sensors and for controlling activation of the heater in accordance with the calculated dewfall temperature.
In a further practical embodiment of the present invention, the low temperature storage cabinet is provided with a surface temperature sensor for detecting a surface temperature of the opening frame structure, wherein the control means is responsive to a detection signal from the surface temperature sensor to activate the heater when the surface temperature of the frame structure is equal to or lower than the calculated dewfall temperature and to deactivate the heater when the surface temperature of the frame structure is higher than the calculated dewfall temperature.